Vehicle headlight control using imaging sensor

ABSTRACT

A vehicle headlamp control method and apparatus includes providing an imaging sensor that senses light in spatially separated regions of a field of view forward of the vehicle. Light levels sensed in individual regions of the field of view are evaluated in order to identify light sources of interest, such as oncoming headlights and leading taillights. The vehicle&#39;s headlights are controlled in response to identifying such particular light sources or absence of such light sources. Spectral signatures of light sources may be examined in order to determine if the spectral signature matches that of particular light sources such as the spectral signatures of headlights or taillights. Sensed light levels may also be evaluated for their spatial distribution in order to identify light sources of interest.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application, Ser. No.09/441,341, filed Nov. 16, 1999 (Attorney Docket DON01 P-770), which isa continuation of U.S. patent application Ser. No. 09/135,565, filedAug. 17, 1998, now U.S. Pat. No. 6,097,023, which is a continuation ofU.S. patent application Ser. No. 08/621,863, filed Mar. 25, 1996, nowU.S. Pat. No. 5,796,094, which is continuation-in-part of U.S. patentapplication Ser. No. 08/023,918 filed Feb. 26, 1993, by KennethSchofield and Mark Larson, now U.S. Pat. No. 5,550,677, and the presentapplication is a continuation-in-part U.S. patent application, Ser. No.11/246,593, filed Oct. 6, 2005 by Schofield et al. for VEHICULAR VISIONSYSTEM (Attorney Docket DON01 P-1244), which is a continuation of U.S.patent application Ser. No. 10/940,700, filed Sep. 14, 2004, now U.S.Pat. No. 6,953,253, which is a continuation of U.S. patent applicationSer. No. 10/372,873, filed Feb. 24, 2003, now U.S. Pat. No. 6,802,617,which is a continuation of U.S. patent application Ser. No. 09/975,232,filed Oct. 11, 2001, now U.S. Pat. No. 6,523,964, which is acontinuation of U.S. patent application Ser. No. 09/227,344, filed Jan.8, 1999, now U.S. Pat. No. 6,302,545, which is a continuation of U.S.patent application Ser. No. 08/478,093, filed on Jun. 7, 1995, now U.S.Pat. No. 5,877,897, which is a continuation-in-part of International PCTApplication No. PCT/US94/01954, which designates the United States andwhich was filed Feb. 25, 1994 and which is a continuation-in-part ofU.S. patent application Ser. No. 08/023,918, filed Feb. 26, 1993, nowU.S. Pat. No. 5,550,677.

BACKGROUND OF THE INVENTION

This invention relates generally to vehicle control systems and, inparticular, to a system and method for controlling the headlights of thevehicles. The invention is particularly adapted to controlling thevehicle's headlamps in response to sensing the headlights of oncomingvehicles and taillights of leading vehicles.

It has long been a goal to automatically control the state of avehicle's headlights in order to accomplish automatically that which ismanually performed by the driver. In particular, the driver of a vehiclewhose headlights are in a high-beam state will dim the headlights uponconscious realization that the headlights are a distraction to thedriver of an oncoming vehicle or a leading vehicle. It is desirable torelieve the driver of such duties and thereby allow the driver toconcentrate on the driving task at hand. The ideal automatic controlwould also facilitate the use of high beams in conditions which allowtheir use, increasing the safety for the controlled vehicle as well asreducing the hazard caused by the occasional failure of the driver todim the headlights when such headlights are distracting another driver.

Prior attempts at vehicle headlight dimming controls have included asingle light sensor which integrates light in the scene forward of thevehicle. When the integrated light exceeds a threshold, the vehicleheadlights are dimmed. Such approaches have been ineffective. Theheadlights of oncoming vehicles are, at least from a distance, pointsources of light. In order to detect such light sources in an integratedscene, it is necessary to set a sufficiently low threshold of detectionthat many non-point-sources at lower intensities are interpreted asheadlights or taillights. Such prior art vehicle headlight dimmingcontrols have also been ineffective at reliably detecting the taillightsof leading vehicles. The apparent reason is that the characteristics ofthese two light sources; for example, intensity, are so different thatdetecting both has been impractical. In order to overcome suchdeficiencies, additional solutions have been attempted, such as the useof infrared filtering, baffling of the optic sensor, and the like. Whilesuch modifications may have improved performance somewhat, the long-feltneed for a commercially useful vehicle headlight dimming control hasgone unmet.

SUMMARY OF THE INVENTION

The present invention provides a vehicle control which is capable ofidentifying unique characteristics of light sources based upon a preciseevaluation of light source characteristics made in each portion of thescene forward of the vehicle, in the vicinity of each light source, byseparating each light source from the remainder of the scene andanalyzing that source to determine its characteristics. Onecharacteristic used in identifying a light source is the spectralcharacteristics of that source which is compared with spectralsignatures of known light sources, such as those of headlights andtaillights. Another characteristic used in identifying a light source isthe spatial layout of the light source. By providing the ability toidentify the headlights of oncoming vehicles and the taillights ofleading vehicles, the state of the headlights of the controlled vehiclemay be adjusted in response to the presence or absence of either ofthese light sources or the intensity of these light sources.

This is accomplished according to an aspect of the invention byproviding an imaging sensor which divides the scene forward of thevehicle into a plurality of spatially separated sensing regions. Acontrol circuit is provided that is responsive to the photosensors inorder to determine if individual regions include light levels having aparticular intensity. The control circuit thereby identifies particularlight sources and provides a control output to the vehicle that is afunction of the light source identified. The control output may controlthe dimmed state of the vehicle's headlamps.

In order to more robustly respond to the different characteristics ofheadlights and taillights, a different exposure period is provided forthe array in order to detect each light source. In particular, theexposure period may be longer for detecting leading taillights andsignificantly shorter for detecting oncoming headlights.

According to another aspect of the invention, a solid-state lightimaging array is provided that is made up of a plurality of sensorsarranged in a matrix on at least one semiconductor substrate. Thelight-imaging array includes at least one spectral separation device,wherein each of the sensors responds to light in a particular spectralregion. The control circuit responds to the plurality of sensors inorder to determine if spatially adjacent regions of the field of viewforward of the vehicle include light of a particular spectral signatureabove a particular intensity level. In this manner, the controlidentifies light sources that are either oncoming headlights or leadingtaillights by identifying such light sources according to their spectralmakeup.

According to another aspect of the invention, a solid-statelight-imaging array is provided that is made up of a plurality ofsensors that divide the scene forward of the vehicle into spatiallyseparated regions, and light sources are identified, at least in part,according to their spatial distribution across the regions. This aspectof the invention is based upon a recognition that headlights of oncomingvehicles and taillights of leading vehicles are of interest to thecontrol, irrespective of separation distance from the controlledvehicle, if the source is on the central axis of travel of the vehicle.Oncoming headlights and leading taillights may also be of interest awayfrom this axis, or off axis, but only if the source has a higherintensity level and is spatially larger. These characteristics ofheadlights and taillights of interest may be taken into consideration byincreasing the resolution of the imaging array along this central axisor by increasing the detection threshold off axis, or both. Such spatialevaluation may be implemented by selecting characteristics of an opticaldevice provided with the imaging sensor, such as providing increasedmagnification central of the forward scene, or providing a widehorizontal view and narrow vertical view, or the like, or by arrangementof the sensing circuitry, or a combination of these.

The present invention provides a vehicle headlight control which isexceptionally discriminating in identifying oncoming headlights andleading taillights in a commercially viable system which ignores othersources of light including streetlights and reflections of thecontrolled vehicle's headlights off signs, road markers, and the like.The present invention further provides a sensor having the ability topreselect data from the scene forward of the vehicle in order to reducethe input data set to optimize subsequent data processing. The inventionis especially adapted for use with, but not limited to, photoarrayimaging sensors, such as CMOS and CCD arrays.

These and other objects, advantages, and features of this invention willbecome apparent upon review of the following specification inconjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation of a portion of a vehicle embodying theinvention;

FIG. 2 is a partial side elevation view and block diagram of a vehicleheadlight dimming control system according to the invention;

FIG. 3 is a block diagram of the control system in FIG. 2;

FIG. 4 is a layout of a light-sensing array useful with the invention;

FIG. 5 is a block diagram of an imaging sensor;

FIG. 6 is an alternative embodiment of an imaging sensor;

FIGS. 7 a-7 d are a flowchart of a control program;

FIGS. 8 a-8 c are spectral charts illustrating spectra regions usefulwith the invention;

FIG. 9 is the same view as FIG. 3 of another alternative embodiment;

FIG. 10 is the same view as FIG. 2 of an alternative mountingarrangement;

FIGS. 11 a-11 c are views forward of a vehicle illustrating differentforms of spatial filtering; and

FIGS. 12 a and 12 b are illustrations of use of the invention to detectparticular atmospheric conditions.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now specifically to the drawings and the illustrativeembodiments depicted therein, a vehicle 10 includes a vehicle headlightdimming control 12 made up of an imaging sensor module 14 which senseslight from a scene forward of vehicle 10, an imaging control circuit 13which receives data from sensor 14, and a vehicle lighting control logicmodule 16 which exchanges data with control circuit 13 and controlsheadlamps 18 for the purpose of modifying the headlight beam (FIGS. 1and 2). Such control may be a binary control of the aim of the beam,such as by switching between lamps or lamp filaments, or may be acontinuous variation of the aim of a single lamp more or less forward ofthe vehicle. The control may also control the intensity or pattern ofthe beam. Additionally, the lights of a vehicle equipped with daytimerunning lights may be switched between a daytime running light conditionand a low-beam condition. Vehicle headlight dimming control 12 canperform a wide range of additional control operations on the vehicle,including turning the headlights ON and OFF, modifying the lightintensity of the instrument panel, and providing an input to anelectro-optic mirror system.

Vehicle lighting control logic module 16 receives an input 20fromimaging control circuit 13. In particular embodiments, such as oneswhich adjust the state of the headlights between continuously variablestates, module 16 may supply data to imaging control circuit 13, such asthe speed of the vehicle, which may be combined with the data sensed byimaging sensor 14 in establishing the state of headlights 18. In theillustrated embodiment, imaging sensor module 14 may be fixedly mountedin a housing 28 by a bracket 34 mounted to, or near, the vehicle'swindshield 32. Bracket 34 also mounts an interior rearview mirror 30.This is a preferred mounting for imaging sensor module 14 because thelocation within the interior of the vehicle substantially eliminatesenvironmental dirt and moisture from fouling the light sensor module.Additionally, the position behind windshield 32, which typically is keptrelatively clear through the use of washers and wipers and the like,ensures a relatively clear view of the scene forward of vehicle 10.Alternatively, imaging sensor module 14 may be mounted within a housing29 of interior rearview mirror 30 facing forward with respect to vehicle10 (FIG. 10). In such embodiment, control circuit 13 may be combinedwith the circuit which controls the partial reflectance level of mirror30 if mirror 30 is an electro-optic mirror such as an electrochromicmirror. Other mounting techniques for sensor module 14 will be apparentto the skilled artisan.

Imaging sensor module 14 includes an optical device 36, such as a lens,an array 38 of photon-accumulating light sensors, and a spectralseparation device for separating light from the scene forward of vehicle10 into a plurality of spectral bands, such as a filter array 40disposed between optical device 36 and light-sensing array 38.Light-sensing array 38 is described in detail in co-pending applicationSer. No. 08/023,918 filed Feb. 26, 1993, by Kenneth Schofield and MarkLarson for an AUTOMATIC REARVIEW MIRROR SYSTEM USING A PHOTOSENSORARRAY, now U.S. Pat. No. 5,550,677, the disclosure of which is herebyincorporated herein by reference. Light-sensing array 36 includes aplurality of photosensor elements 42 arranged in a matrix of columns androws (FIG. 4). In the illustrated embodiment, an array of 512 rows and512 columns of light-sensing pixels, each made up of a photosensorelement 42 is utilized. However, a greater or lesser number ofphotosensor elements may be utilized and may be arranged in matrix thatis laid out in other than columns and rows. Each photosensor element 42is connected to a common word-line 44. To access the photosensor array,a vertical shift register 46 generates word-line signals to eachword-line 44 to enable each row of photosensor elements 42. Each columnof photosensor elements is also connected to a bit-line 48 which isconnected to an amplifier 50. As each word-line 44 is accessed, ahorizontal shift register 52 uses a line 54 to output the bit-linesignals on consecutive bit lines 48 to an output line 56. In thismanner, each photosensor element 42 may be individually accessed byappropriate manipulation of shift registers 46 and 52. Output 56 issupplied to a digital signal processor 13 which is supplied on an output62 as input to control circuit 13 (FIGS. 3-5).

Digital signal processor 13 includes an analog-to-digital converter 58which receives the output 56 of array 36 and converts the analog pixelvalues to digital values. A digital output 68 of A/D converter 58 issupplied to a taillight detection circuit 76, a headlight detectioncircuit 78, and to ambient sense logic circuit 84. A detection controlcircuit 72 supplies control and timing signals on a line 74 which issupplied to array 38, A/D converter 58 taillight detection circuit 76,headlight detection circuit 78, and ambient sense logic 84. Such signalscoordinate the activities of these modules and provide any data, fromlook-up tables provided in control circuit 72, needed by each circuit toperform its function. For example, control circuit 72 may provideintensity threshold levels to taillight detection circuit 76 andheadlight detection circuit 78.

Taillight detection circuit 76 detects a red light source having anintensity above a particular threshold as follows. For each pixel thatis “red,” a comparison is made with adjacent “green” pixels and “blue”pixels. If the intensity of a red pixel is more than a particular numberof times the intensity of the adjacent green pixel and adjacent bluepixel, then it is determined that the light source is red. If theintensity of the “red” light source is greater than a particularthreshold, an indication is provided at 80.

Headlight detection circuit 78 detects a white light source having anintensity above a particular threshold as follows. A white light is acombination of red, green, and blue components. If adjacent “red,”“green,” and “blue” pixels all exceed a particular threshold, a ratiocomparison is made of the pixels. If the ratio of the intensity of theadjacent “red,” “green,” and “blue” pixels is within a particular range,such as 20 percent by way of example, then a white light source isdetected.

Vehicle headlight dimming control 12 additionally includes an ambientlight-sensing circuit 84 which receives an input from digital outputsignal 68. Ambient detection circuit 84 samples a subset of photosensorelements and detects light levels sensed by the subset over a longperiod of time in order to produce significant time filtration.Preferably, the photosensor elements in the sensed subset includesensors that detect portions of the forward-looking scene that are justabove the earth's horizon which is more indicative of the ambient lightcondition. Ambient detection circuit 84 produces an indication 88 ofambient light levels which is supplied as an input to a lighting controlmodule 90. A high ambient light level may be used by a module 90 toinhibit headlight actuation or to switch headlights 18 to a daytimerunning light mode. Ambient detection circuit 84 can, optionally,perform other functions, such as switching the daytime running lights ofthe vehicle between daytime and nighttime modes, controlling theintensity of the vehicle's instrument panel and providing an input to anelectro-optic rearview mirror system.

Indications 80 and 82 from the light detection units and indication 88from ambient detection circuit 84 are supplied to a lighting controlcircuit 90 which produces a first indication 92 that headlights 18 areto be switched on, or switched from a daytime running condition to anight mode, and a high-beam enable indication 94 that the headlights maybe switched to a high-beam state. Vehicle lighting control logic module16 responds to indications 92 and 94 by switching headlights 18 to anappropriate mode. An output 96 from module 16 may be provided to supplylighting control circuit 90 with information with respect to vehicletelemetry, steering, speed, and any other parameter that may beincorporated into the algorithm to determine the state of the headlightsof the vehicle. Digital signal processor 13 may be implemented usingdiscrete digital circuit modules or with a suitably programmedmicro-processor with input and output buffers.

In one embodiment, an imaging sensor module 14 a includes a singlephotosensor array 38 a, one spectral filter array 40 a, and one opticaldevice 36 a (FIG. 5). In this illustrated embodiment, spectral filterarray 40 a includes alternating spectrum filter elements for exposingadjacent pixels to different regions of the electromagnetic spectrum inthe red band or green band or blue band. This may be accomplished byarranging such filter elements in stripes or by alternating filterspectral regions in a manner known in the art. Digital signal processor13 a captures a frame of data by enabling photosensor array 38 a for aparticular exposure period during which each photosensor element 42accumulates photons. In order to detect oncoming headlights, digitalsignal processor 13 a enables photosensor array 38 a for a firstexposure period. In order to detect leading taillights, digital signalprocessor 13 a enables photosensor array 38 a for a second exposureperiod. Because oncoming headlights have an intensity level that issubstantially greater than that of leading taillights, the exposureperiod of the frame in which leading taillights is detected is at leastapproximately ten times the length of the exposure period during whichoncoming headlights are detected. Most preferably, the exposure periodfor detecting leading taillights is approximately 40 times the exposureperiod for detecting oncoming headlights. In the illustrated embodiment,an exposure period of 0.004 seconds is utilized for detecting taillampsand 0.0001 seconds for detecting oncoming headlamps. The exposure periodis the time during which each photosensor element 42 integrates photonsbefore being read and reset by digital signal processor 13 a.Establishing a different exposure period for detecting headlights versestaillights facilitates the use of existing and anticipated sensortechnology by accommodating the dynamic range of such sensor technology.Exposure may also be adaptively established on a priority basis. In onesuch embodiment, exposure is set to a shorter headlight setting. Ifheadlights are detected, the headlights 18 of vehicle 10 are dimmed andthe exposure period is kept short. If no headlights are detected, thenext frame is set to a longer exposure period. This has the advantage ofshorter system cycle time as well as a reduction in sensitivity tosensor saturation and blooming. In another such embodiment, the exposureperiod is initially set to a long period. If an oncoming headlight istentatively detected, the exposure period could then be switched to ashort period to confirm the observation.

Vehicle headlight dimming control 12 carries out a control routine 100(FIGS. 7 a-7 d). At the beginning of each pass through the routine,which occurs for every frame captured by the imaging sensor, a frame isgrabbed at 102 and all of the pixels in the frame are processed asfollows. Counters used for detecting white headlight sources and redtaillight sources are zeroed at 104. It is then determined at 106whether the previously processed frame was for detecting headlights ortaillights. This is determined by looking at a variable “process tails”which will be set to “yes” if the previous frame was processed to detectheadlights and will be set to “no” if the previous frame was processedto detect taillights. If it is determined at 106 that the variable“process.tails” is set to “yes,” the control proceeds to 108 in order toprocess the next frame to detect taillights. If it is determined at 106that the variable process tails is set to “no,” then control passes to109 in order to process the next frame as a headlight detecting frame.

The taillight detecting frame process begins at 108 by setting theexposure period for the imaging sensor module to grab the next frameaccording to a headlamp exposure level. In the illustrated embodiment,the exposure period for detecting headlights is set at 0.0001 seconds.Processing of the taillight frame proceeds at 110 by examining, for each“red” pixel, whether the intensity of light sensed by that pixel isgreater than a threshold and whether the intensity of light sensed bythat pixel is greater than a selected number of multiples of theintensity of light sensed by an adjacent “blue” pixel and a selectednumber of multiples of the intensity of light sensed by an adjacent“green” pixel. If so, then a “red” counter is incremented at 114.Preferably, the ratio of red pixel intensity to green or blue pixelintensity is selected as a power of 2 (2, 4, 8, 16 . . . ) in order toease digital processing. However, other ratios may be used and differentratios can be used between red/green and red/blue pixels. In theillustrated embodiment, a ratio of 4 is selected based upon ratiosestablished from CIE illuminant charts known to skilled artisans. Basedupon these charts, a ratio greater than 4 would provide greaterdiscrimination. Such greater discrimination may not be desirable becauseit could result in failure to identify a leading taillight and, thereby,a failure to dim the headlights of the controlled vehicle. After allpixels have been processed, the parameter “process.tails” is set to “no”at 116 and control proceeds to 118 (FIG. 7 c).

In a similar fashion, processing of a headlight frame begins at 110 bysetting the exposure period for the imaging sensor module to grab thenext frame as a red taillight detecting frame. This is accomplished bysetting the exposure period of the imaging sensor module to 0.004seconds. It is then determined at 120 for each pixel whether an adjacentset of “red,” “green,” and “blue” pixels each exceeds a particularthreshold and whether the pixel intensity levels all fall within aparticular range, such as within 20 percent of each other. If all of thered, green, and blue pixels exceed a threshold and pass the ratio test,then it is determined that a white light source is being sensed and a“white” counter is incremented at 122. After all of the pixels in theframe have been processed, the process.tails flag is set to a “yes”state at 124. Control then passes to 118.

It is determined at 118 whether both the “white” and the “red” countersare below respective high-beam thresholds. If so, a high-beam framecounter is incremented and a low-beam frame counter is set to zero at120. If it is determined at 118 that both the “white” and the “red”counters are not less than a threshold, it is then determined at 126whether either the “red” counter or the “white” counter is greater thana respective low-beam threshold. If so, the high-beam frame counter isset to zero and the low-beam frame counter is incremented at 128. If itis determined at 126 that neither the “red” counter or the “white”counter is greater than the respective low-beam threshold, then both thehigh-beam frame counters and the low-beam frame counters are set to zeroat 130.

Control then passes to 132 where it is determined if the low-beam framecounter is greater than a particular threshold. If so, high-beam enablesignal 94 is set to a “low-beam” state at 134. Additionally, thelow-beam frame counter is set to the threshold level. If it isdetermined at 132 that the low-beam frame counter is not greater thanits threshold, it is determined at 136 whether the high-beam framecounter is greater than its threshold. If so, high-beam enable signal 94is set to “high-beam” state at 138 and the high-beam frame counter isreset to its threshold level.

Control routine 100 provides hysteresis by requiring that a headlightspectral signature or a taillight spectral signature be detected for anumber of frames prior to switching the headlights to a low-beam state.Likewise, the absence of a detection of an oncoming headlight or aleading taillight must be made for multiple frames in order to switchfrom a low-beam to a high-beam state. This hysteresis guards againsterroneous detection due to noise in a given frame and eliminatesheadlamp toggling when sources are at the fringe of detection range. Inthe illustrated embodiment, it is expected that a vehicle headlightcontrol system 12 will respond to a change in the state of light sourcesin the forward field of view of the vehicle in less than 0.5 seconds. Anadditional level of hysteresis may be provided by forcing the headlampsto stay in a low-beam state for a given number of seconds after atransition from high beams to low beams. The reverse would not occur;namely, holding a high-beam state for a particular period to avoidannoyance to drivers of oncoming or leading vehicles.

In the illustrated embodiment, red light sources, which have thespectral signature and intensity of taillights, are detected bydetermining that a “red” pixel, namely a pixel which is exposed to lightin the visible red band, is both greater than a given multiple of the“green” and “blue” adjacent pixels, as well as being greater than athreshold and that white light sources, which are the spectralsignatures of headlights, are detected by determining that “red,”“green,” and “blue” pixels are both within a particular intensity rangeof each other as well as being greater than a threshold. Thisdouble-testing helps to reduce false detection of light sources.However, it would be possible to detect red light sources only bylooking at the intensity of “red” pixels and to detect white lightsources by determining that an adjacent set of “red,” “blue,” and“green” pixels are all above a particular threshold.

In the illustrated embodiment, spectral filtering is carried out in amanner which exposes each photosensing element in the photosensor arrayto a band of light falling within one of the primary ranges of thevisible spectrum, namely red, green, or blue as illustrated in FIG. 8 a.However, different bands in the frequency spectrum may be utilizedincluding not only visible spectrum bands but invisible spectrum bandsincluding infrared and ultraviolet bands as illustrated in FIG. 8 b. Theband selection could also be chosen from visible spectral regions thatdo not correspond with the primary spectrums. For example, the spectralfilter may be selected in order to detect at the pixel level red lightsources and the complement of red light sources as illustrated in FIG. 8c. These binary indications could be utilized to detect red taillightsby determining that the “red” pixel is greater than a threshold andgreater than a number of multiples of the intensity sensed by the “redcomplement” pixel adjacent thereto. Likewise, a white light sourceindicative of oncoming headlights could be detected by determining thatboth the “red” pixel and the “red complement” pixel adjacent thereto areboth above a particular threshold and within a particular intensityrange of each other. It may also be desirable to select bands that fallbetween primary spectrum regions or any other bands that may bedesirable for a particular application.

Photosensing array 38 may be a charge couple device (CCD) array of thetype commonly utilized in video camcorders and the like. Alternatively,photosensing array 38 could be a CMOS array of the type manufactured byVLSI Vision Ltd. (VVL) in Edinburgh, Scotland. Additionally, a hybrid ofthe CCD and CMOS technology may be employed. Other potentially usefulphotosensing technologies include CID, MOS, photo diodes, and the like.

In an alternative embodiment, an imaging sensor module 14 b includes twoor more pairs of photosensor arrays 38 b (FIG. 6). Each photosensorarray 38 b has an associated spectral filter array 40 band opticaldevice 36 b. In this embodiment, each array 38 b is operated by digitalsignal processor 58 b to have an exposure period that is set fordetecting either oncoming headlights or leading taillights. In thismanner, each frame of the scene captured by each array is utilized todetect a particular light source. This is in contrast to light-sensingmodule 14 a in FIG. 5 in which each light source is detected inalternating frames. Each spectral filter 40 b is identical, whereby eacharray 38 b is capable of detecting light sources having spectrumcomposition including red, green, and blue regions of the spectrum.However, the spectral filters may be custom configured to the particularapplication. This may result in a homogeneous composition or a morecomplex mosaic, especially where light sources are examined in three ormore spectral regions.

In yet an additional single lens system embodiment, an imaging sensormodule 14 c includes three light-sensing arrays (not shown) and aspectral separation device overlying the light-sensing arrays whichdirects spectral bands to different arrays (FIG. 9). An example of suchspectral separation device is a refracting optical splitter, such asdichroic mirrors or prisms. In this manner, each light-sensing arraydetects light in either the red or green or blue region of the spectrum.As such, imaging sensor module 14c produces three output signals on aline 64, each representing detected light in one of the red or green orblue spectral regions. The output signals on line 64 includeframe-timing signals which are decoded by digital acquisition circuits66 which produces a digital output signal 68′ indicative of intensitylevels of adjacent red, green, and blue pixels. Digital acquisitioncircuit 66 additionally produces a timing signal output 70 which isutilized by a detection control circuit 72 in order to supplysynchronizing signals, at 74, to imaging sensor module 14 c and digitalacquisition circuit 66. A control and timing signal 86 is produced bydigital acquisition circuit 66 and supplied to detection circuits 76 and78 and ambient detection circuit 84 in order to enable the circuits todistinguish between subsequent frames captured by the light-sensingmodules. As with previously described embodiments, digital output signal68′ is supplied to taillight detection circuit 76, headlight detectioncircuit 78, and ambient sense logic circuit 84.

The present invention is capable of identifying point sources of lightin any particular location within the scene viewed forward of thevehicle. Additional discrimination between oncoming headlights andleading taillights may be accomplished by taking into account therelative location of the source of light within the scene. For example,as best seen by reference to FIG. 11 a, particular relationships havebeen discovered to exist between light sources of interest and theirspatial location forward of the vehicle. Oncoming headlights and leadingtaillights of interest can be characterized, at least in part, basedupon their displacement from the central axis of the vehicle. On-axislight sources of interest can be at both close and far away separationdistances. However, off-axis light sources may only be of interest if ata close separation distance from the vehicle. Assuming for illustrationpurposes that headlights and taillights are of the same size, headlightsand taillights of interest occupy an increasing spatial area as theymove off axis. Therefore, the resolution required to detect lights ofinterest may decrease off axis. Additionally, the fact that close-upoff-axis light sources have significant spatial area would allowimage-processing techniques to be employed to discriminate betweenclose-up off-axis light sources of interest and distant off-axis lightsources, which are not of interest. This may be accomplished throughcustomized optics or other known variations in pixel resolution.Furthermore, headlights and taillights of interest are of greaterintensity, because of their closeness, off axis. This allows an increasein intensity detection thresholds off axis without missing detection ofsuch light sources. This increase in detection threshold and reductionin resolution off axis assists in avoiding false detection of lightsources not of interest, such as a streetlights, building lights, andthe like.

In order to take into account this spatial differentiation, the presentinvention comprehends detecting light sources at a lower thresholdcentrally of the scene and at a higher threshold at the periphery of thescene. This may be accomplished either optically, or electronically, orboth. Optically, this may be accomplished by providing a non-uniformmagnification to optical device 36. For example, an optical device mayhave optical magnification at a central portion thereof and an opticalattenuation at a peripheral region thereof. Additionally, optical device36 may have a relatively wide horizontal field of view and a relativelynarrow vertical field of view. The narrow vertical field of view wouldtend to reduce the detection of street lights and other overhead lightsources. In a preferred embodiment, optical device 36 is a lens that ismade from injection-molded plastic. Electronically, such spatialdifferentiation may be accomplished by establishing a higher thresholdlevel for pixel intensity detection for pixels located at the peripheryof the scene than for pixels located centrally of the scene. This wouldcause centrally positioned light sources to be detected at a lowerintensity level than sources detected at the periphery of the scene.Such spatial differentiation could also be accomplished by anon-symrnmetrical mapping of light to the sensor array, as illustratedin FIG. 11 b, or by masking portions 98 a, 98 b, and 98 c, at theperiphery of the scene, as illustrated in FIG. 11 c, so that theseportions are not sensed at all. Spatial differentiation could also beaccomplished by providing non-uniform pixel size.

The present invention is exceptionally sensitive to sources of lighthaving spectral signatures of oncoming headlights and leadingtaillights. By recognizing the spectral signature of the light sources,many non-relevant light sources may be ignored. By examining lightsources pixel-by-pixel, relatively small light sources may be detectedat great distances in order to dim the headlights well before theybecome a nuisance to the driver of the vehicle ahead of the controlvehicle. This is accomplished, according to a preferred embodiment, byutilizing an imaging sensor made up of an array of photosensing elementsin a compact design which responds to light sources in a scene forwardof the vehicle. Furthermore, such sensor preferably utilizes digitalprocessing techniques which are well adapted for use with custom digitalelectronic circuity, avoiding the expense and speed constraints ofgeneral purpose programmable microprocessors.

The present invention takes advantage of the spectral signatures both oflight sources which must be detected in a headlight dimming control aswell as the spectral signatures of light sources which must be rejectedin a headlight dimming control. For example, federal regulationsestablish specific spectral bands that must be utilized in vehicletaillights; namely red. Furthermore, federal legislation prohibits theuse of red light sources in the vicinity of a highway. Lane markers,signs, and other sources of reflected light are all specified in amanner which may be readily identified by spectral signature. Oncomingheadlights, according to known technology, have a visible spectralsignature which is predominantly white light. As light source technologyevolves, the present invention facilitates detection of other spectralsignatures of light sources in the future.

The present invention is capable of utilizing spatial filtering to evenfurther enhance the ability to identify light sources. By spatialfiltering is meant consideration of not only whether a particular pixel,or pixel group, is detecting a light source having a particular spectralsignature, but also what adjacent, or closely related, pixels or pixelgroups, are detecting. For example, it can be concluded that veryclosely adjacent red and white light sources are not of interest asoncoming headlights or taillights. An example where such pattern couldbe observed is a streetlight observed with a system having imperfectcolor correction, which can produce a white light surrounded by a redhalo. By evaluation of adjacent pixel groups, a closely proximate redlight source and white light source can be identified as a streetlightand not either a headlight or a taillight.

Pattern recognition may be used to further assist in the detection ofheadlights, taillights, and other objects of interest. Patternrecognition identifies objects of interest based upon their shape,reflectivity, luminance, and spectral characteristics. For example, thefact that headlights and taillights usually occur in pairs could be usedto assist in qualifying or disqualifying objects as headlights andtaillights. By looking for a triad pattern, including the centerhigh-mounted stoplight required on the rear of vehicles, stoplightrecognition can be enhanced. Furthermore, object recognition can beenhanced by comparing identified objects over successive frames. Thistemporal processing can yield information on object motion and can beused to assist in qualifying or disqualifying objects of interest.

Spatial filtering can also be useful in identifying atmosphericconditions by detecting effects on light sources caused by particulartypes of atmospheric conditions. One such atmospheric condition is fog.A bright light source 102 is surrounded by a transition region 104between the intensity of the light source and the black background (FIG.12 a). Fog, or fine rain, tends to produce a dispersion effect aroundlight sources which causes a series of transition regions 104 a, 104 b .. . 104 n which extend further from the light source (FIG. 12 b). Byplacing appropriate limits on the size of the transition region, fog orlight rain, or a mixture of both, or other related atmosphericconditions, can be detected. In response to such atmospheric conditions,vehicle headlight dimming control 12 may activate fog lights, inhibitswitching to high beams, or perform other control functions.Furthermore, fog, or fine rain, can be detected, or confirmed, byanalyzing the effects of headlights 18 in the forward scene as reflectedoff of moisture particles.

Spatial filtering can also be used to detect rain on windshield 32. Thismay be accomplished by performing statistical analyses between a pixel,or pixel group, and adjacent pixels or pixel groups. A view forward of avehicle through a dry windshield would be sensed by an imaging sensormodule as continuously varying differences between adjacent pixels, orpixel groups, assumed to be under constant illumination from lightsources. When, however, a droplet of water or a snowflake is onwindshield 32, an effect is created which causes a lack of continuousvariation of differences between adjacent pixels, or pixel groups. Thishas the tendency to reduce the first derivative of the pixel, acondition which can be determined by processing.

Processing can be used to determine the first derivative of an imagecaptured by image-sensing module 14 by determining a measure of theentropy, or disarray, of a pixel, or pixel group, with respect to itsneighbors. For example, an approximation of the first$\frac{\mathbb{d}\left( P_{i} \right)}{\mathbb{d}{xy}} = \frac{\sqrt{\sum\limits_{j = 1}^{n}}\left( {{Pi} - {Pj}} \right)^{2}}{N}$derivative for a pixel is:

where N=8 and

where Pi is a given pixel and Pj is one of 8 neighboring pixels.

It should be apparent to those skilled in the art that the invention iscapable of performing control functions other than controlling thedimming of the vehicle's headlights. For example, spectral signatureidentifications may be utilized to detect the state of a traffic lightto either warn the driver that a light has changed from green to yellowto red or to automatically decelerate and stop the vehicle. Also, bysensing that the intensity of a leading taillight has abruptlyincreased, a condition where the leading vehicle is braking may beidentified and suitable action taken.

The invention may be utilized to identify particular traffic signs bytheir spectral signature as well as their geometric organization. Forexample, red octagons may be identified as stop signs, yellow trianglesas caution signs, and the like. These capabilities are a result of thepresent invention providing a significant reduction in the amount ofdata to be processed because the image forward of the vehicle iscaptured in a manner which preselects data. Preselection of data isaccomplished by configuring the sensor array, including the opticsthereof, to consider the spatial, as well as the spectral,characteristics of light sources.

The present invention may be used to determine the environment in whichthe vehicle is operated. For example, a high level of “non-qualified”light sources; namely, light sources that are not headlights ortaillights, as well as “qualified” light sources can be used todetermine a measurement of the activity level around the vehicle;namely, that the vehicle is in an urban environment which may be auseful input for particular control algorithms. This may be accomplishedas follows. An activity counter is established which represents a totalnumber of pixels, or pixel groups, whose red, green, or blue componentsexceed a threshold. The threshold is set to a relatively low value,namely just above the noise floor. This counter, which registers anyreal detected source, is reset and retabulated every frame, preferablyduring the exposure period for detecting taillights. If the activitycounter exceeds a particular value, then a high activity environment isdetected. One use of this information would be to inhibit the controlfrom switching the vehicle's headlights from a low-beam state to ahigh-beam state unless a low activity condition exists for awhile. Theactivity counter may be used by the control in combination with alow-beam duration counter which records the number of frames that thesystem has been in a low-beam state. It is reset upon system power-upand at every transition from the high-to-low beam states. The controlmay be inhibited from switching the vehicle's headlights to thehigh-beam state unless either the low-beam duration counter exceeds avalue or the activity counter indicates a sustained low activitycondition.

The present invention can be used to detect lane markers in order toeither assist in steering the vehicle or provide a warning to the driverthat a lane change is occurring. The capability of the invention todetect rain on the vehicle's windshield could be used to control thevehicle's wipers both between OFF and ON conditions and to establish afrequency of intermittent operation.

Changes and modifications in the specifically described embodiments canbe carried out without departing from the principles of the inventionwhich is intended to be limited only by the scope of the appendedclaims, as interpreted according to the principles of patent lawincluding the doctrine of equivalents.

1. A vehicle headlamp control, comprising: an imaging sensor that senseslight in spatially separated regions of a field of view forward of avehicle; and a control circuit that is responsive to said imaging sensorin order to determine if individual regions of the field of view includelight levels having a particular intensity level in order to identifylight sources of interest and provide a control output to said vehiclethat is a function of the identification of light sources of interest.